A hot-rolled steel sheet after finish rolling of a hot-rolling process is cooled by a cooling apparatus provided above and below a run-out table to a predetermined temperature while being transported by the run-out table from a finishing mill to a coiler, and is thereafter coiled by the coiler. In the hot rolling of the hot-rolled steel sheet, cooling manners after the finish rolling are important factors that determine mechanical properties, workability, weldability, and the like of the hot-rolled steel sheet, and thus it is important to uniformly cool the hot-rolled steel sheet to a predetermined temperature.
In the cooling process after the finish rolling, typically, the hot-rolled steel sheet is cooled by using, for example, water (hereinafter, called cooling water) as a coolant. Specifically, in a predetermined cooling area of the hot-rolled steel sheet, the hot-rolled steel sheet is cooled by using the cooling water. In addition, as described above, in order to uniformly cool the hot-rolled steel sheet to a predetermined temperature, there is a need to prevent extra cooling water on the upstream side or the downstream side of the cooling area from leaking.
Therefore, blocking the cooling water on the hot-rolled steel sheet is performed. As a water-blocking method for the cooling water, various methods have been proposed.
In Patent Document 1, arranging one or more rows of nozzles that spray water-blocking water from slit-shaped or circular nozzle spray holes on the downstream side of a cooling apparatus, that is, cooling nozzles that spray cooling water so that spray angles thereof are inclined toward the upstream side of a hot-rolled steel sheet in a sheet-threading direction is proposed. In addition, blocking the cooling water is performed by the water-blocking water sprayed onto the hot-rolled steel sheet from the nozzles.
In addition, in Patent Document 2, providing a water spray type water-blocking facility in a cooling apparatus and arranging air nozzle groups on the downstream side of the water spray type water-blocking facility is proposed. In addition, water-blocking water is sprayed onto a hot-rolled steel sheet from the water spray type water-blocking facility, and air is simultaneously ejected toward the hot-rolled steel sheet from the air nozzle groups in an air wind direction substantially perpendicular to a sheet-threading direction, thereby blocking the cooling water is performed.
Moreover, in Patent Document 3, a water-blocking apparatus which includes a header provided with nozzles that spray water-blocking water onto a hot-rolled steel sheet so that a momentum of the water-blocking water per unit time and unit width (a force of the water-blocking water) is maintained in a range of 1.5 to 5 times the momentum of cooling water that stays on the surface of the hot-rolled steel sheet per unit time and unit width (a force of the cooling water) to spray the water-blocking water onto the hot-rolled steel sheet from the nozzles is proposed.